Improved mechanical properties of near-eutectic Al-Si piston alloy through ultrasonic melt treatment

The effects of ultrasonic melt treatment (UST) on the microstructure and mechanical properties of Al-12.2Si-3.3Cu-2.4Ni-0.8Mg-0.1Fe (wt%) piston alloy were systematically investigated. Rigid colonies consisting of primary Si, eutectic Si, Mg2Si and various aluminides (ε-Al3Ni, δ-Al3CuNi, π-Al8FeMg3Si6, γ-Al7Cu4Ni, Q-Al5Cu2Mg8Si6 and θ-Al2Cu) were observed in the as-cast alloys. The sizes of the secondary phases, eutectic cell and grain were significantly decreased by UST because of the enhanced nucleation of each phase under ultrasonic irradiation. The yield strength, tensile strength and elongation at 25 °C were significantly improved by UST mainly because of the refinement of the microstructures. Both tensile strength and elongation at 350 °C were also improved by UST despite the unchanged yield strength.